Many polyamorous people were serial monogamists beforehand and perhaps due to a situation where they’ve had to chose between 2 people whom they love equally, have come to the conclusion that monogamy encourages emotional hurt and exacerbates rather than abates destructive forms of jealousy and a toxic sense of propriety.
Many eschew the Judeo-Christian definition of a loving relationship as being an exclusive pact between a woman and a man as damaging to mental well-being, and they often liken it to a hypothetical situation whereby a friend exercises a proprietory claim over a person, forbidding them to have any other friends or do anything friendly with other people except them. The argument goes, if you think such a situation is ridiculous, why do you then accept that jealousy within a romantic-sexual relationship is perfectly normal and healthy?
Sexual jealousy is the only negative emotion which we encourage in our society. If someone is feeling jealous of their partner, as a society we give them the benefit of the doubt them even if they manipulate others in that jealous rage. We find ourselves cheering on the jealous partner in those “Ricky Lake/Jeremy Kyle”-type programmes while at the same time teaching our children that jealousy is wrong, and encouraging them to share. In some countries, a “crime of passion” gets a lower sentence. If it were anger, greed or cruelty that inspired the crime, we wouldn’t be so forgiving, but when the motive is sexual jealousy, we somehow feel that it gives people carte blanche to do what they want with impunity.
The root of this unhealthy pathology in our society is that when we are children, we are taught to control our negative emotions and we learn that you cannot use them to manipulate others, but we also tacitly imply that jealousy is an exception, that it is fine and healthy.
Polyamorous people instead aspire to show a special form of empathy known as “compersion” (a word which you probably won’t find in a dictionary but you can find defined in the Urban Dictionary, and in a Huffington Post article).